Method for inhibiting roll pickup in continuous annealing of steel strip



March 2, 1954 D. c. BLAIR ET AL 2,671,038

METHOD FOR INHIBITINO ROLL PICKUP IN CONTINUOUS ANNEALING OE STEEL STRIP mea Jan. EO, 195s Patented Mar. 2, 1954 Y '-METnoD Fon INHIBITING ROLL AProlineh 1N CONTINUOUS ANNEALING oF STEEL STRIP David Blair,WashingtonvTovvnshipQWestinoez t landwConnty; andjjHarry F. Shannon, Mountv f A Lebanon Township, Allegheny Countafa., asf

This invention relateso tlie "continuous heattreatment of fiat-rolled metal products and, in particular, to provisions for inhibiting the building up of accretions of oxides on the rolls which ignorsteUniteaifstates steeli -co rpomipn;

A complete understanding ofthe inventiorrmay be obtained from the. f ollow ing. detaileddescrilza-` tion. and explanation "thereof hich' ref er .tothe accompanying drawings ilus rating] support the products during travel through a embodiment and'a`mod1 atn e drawcontinuous annealing furnace. Y ings," V vQ Great diiiicultyY has been'experienced in th Figire' 1i Ais af' central lo' E continuous annealing of ferrous strip, and parlargely. diagrammatic, thr gli a strip-annealing ticularly silicon-steelstrip, because of thetendfurnace embodying the p aratmfadabted! for ency of the furnace r o ll s over which the-strip carrying out the methodofo" mv'ention f passes, topick up Vadligereni;accretions 'of oxides 'Figure 2 is a partialfyetical`-.section talig? which buildup quickly to s uch a form and'extent along the plane of line II-II fFi'g'ure'l and` that they mark'the strip the manner known .Figure 3 .is a transverse section throu on 0f as dimpling. The rolls areusually composed the conveyor'rolls anditsassoc'at' l of vordinary steel or a heat-resistant alloy. Appipe, taken along-the"planel parently, particles composed ofthe mixed oxides Figure 2. of iron and silicon adhere to theffurnace-"con- 'Referring in detail tp the raw g `s veyor rolls during the annealingprocess. As the the present,'to Figure 1 --a s annealing campaign progresses, these particles, nace indicated generallya I-ll co rnpri ses arecornmonly called pick-up, increase in size to fractory-lined enclosure laidjup. withinafconv'e'nsuch an extent that thev L'strip passing Aover the tional binding fabricated-from steelplate-and roll is marked or dimpled rendering it unsuitrolled sections (not sho w r'l njtheknoWnmam able for most applications. When this occurs, ner. The furnace has an entrance opening II usually in from several hours to several days, at one end and an exit opening I2 at the other, depending on the composition of the furnace atadapted to permit the passage of strip theremosphere, the furnace must be cooled to approxithrough from an uncoiler at the entrance end mately room temperature and the particles reto a recoiler at the exit end. The furnace may moved from the rolls by mechanical means. A be heated by any suitable means, i. e., electric great loss of production results and the increased resistors, radiant combustion tubes or the like. costs of processing thus involved are serious. A controlled atmosphere, usually decarburizing,

We have invented a novel method for inhibitis supplied to the furnace chamber by any coning the pick-up of oxide particles by the furnace venient means (not shown) rolls, thus almost eliminating the necessity for In order to maintain each point along the strip periodically shutting down the furnace to 4clean at the temperature necessary to produce decarthe rolls or greatly reducing the frequency thereburization, for the required length of time, the of. In a preferred practice, We discharge streams strip is trained alternately over conveyor rolls of reducing gas onto the surface of the strip I3 in an upper series designated I3 and a lower ahead of the points of contact with the rolls. series designated I3b. The rolls I3 have shafts This not only prevents the formation of oxides I4 extending through the side walls of the furbut tends to reduce any oxides already formed nace and journaled in any suitable bearings caron the strip and keeps the rolls free from acried thereby. The shafts are driven in the known cumulating accretions or pick-up. The preferred manner by any convenient mechanism. The arapparatus comprises a manifold or nozzle pipe rangement of the rolls in the two series as shown disposed in the V between the body of the conis such that the strip, when properly trained veyor roll and strip approaching it. The pipe thereover is caused to make a plurality of passes is connected to a supply of a suitable gas and upwardly and downwardly throughout substanis provided with nozzles or outlet ports spaced tially the full height of the chamber. 'I'he cytherealong, discharging into the V. Any reduclindrical bodies of rolls I3 may be fabricated ing gas such as hydrogen, methane or carbon from steel plate. Instead of a unitary cylinder, monoxide may be used for strip generally but, the roll bodies may consist of a plurality of discs for silicon-steel strip, an atmosphere largely of spaced along the shaft. hydrogen is preferable because the other gases A manifold or nozzle pipe I5 is disposed admentioned tend to recarburize the strip whereas jacent each roll I3, preferably in the V between decarburization is often an important objective the cylindrical roll body and the portion of thel of the annealing practice. 56 strip I6 approaching it. The manifolds I5 are connected by piping to any suitable source of reducing gas (not shown) and are provided with outlet ports I7 spaced therealong. 'I'he manifolds are preferably of heat-resistant alloy and are positioned sothat their porrts disharge jets of redueig 'gasfbiitoltiie surface f tue-strip ahead of' l`th point f contact the with the rolls. Any suitable means may be provided for supporting the manifolds in the proper position relative to the conveyor rolls I'Buch fas 'brackets of heat-resistant meta-l. Y l' The reducing gas may be of any desired character depending on the av'aii'abie fsoiires-. drogen is particularly effective Carlo' inonoxide and methane may also h'ise'c'l 'Where their carburizing property is not objectionable. Cracked ammonia gas containing about 'v5%`hy drogen and 25% nitrogen Seive'svry satisfacitorily but the gas must have a net reducing effect since tests with neutral gas such as nitg'en do not give the desired result in preventing roll DQkll). YThe reducing 'gas appears to exert t'wmi'lii eirect m thatit tends te reduce any oxides present un Kme strip which are' the source 'of m11, piek.- up, and also locally cools', any uiireduced oxides below the temperature at which they adhere to the rolls. lhe rduc'in'gfga-s should not be "supplied in sufcint quantity to alter the noriiia-lly slightly oxidizing charac'tevof the 'furnace atmosphere asa vWhole, which is ne'es'sary toeffect the decarburiation desired in the case of siliconsteel strip. n H i i l *Elxperience` indicates that the invention prmits furnace rolls 't -operatwithot objection'- i atie piek-opfer peridspto one hundred mines as great as thosel in which pick-up would other- Wise occur to aexteht Aas to cause diir'iplihg of the strip; The invention thus has the' advantage 'of greatly reducing the iss f production and the expense involved iii shutting down stripaneaiing furnaces for cleaning piek-up frm me conveyr relis therein?.l

Although We have disclosed herein the preferred embodiment of our invention, we intend to cover as Well any change or modication therein which may be made Without departing frorni the spirit and scope.) of. the invention.

'Wiscaiz Y i a In a retho'd hdf annealing silicon-steel strip which, at annealing temperatures, leaves accmulations of mixed oxides of iron and silicon `afd'herin'g to "conveyor rolls over which it travels, th- 'steps including passing the strip through a. heating zone'containing a normally oxidizing atni'osphere, "over 'supporting rolls, and introducing "a reduiirigfghs directly into the V-shaped fs betvveeirithesurfaces of the rolls and the porJ l s of the strip approaching them, at a plurality of pointspaced across the width of the strip-therhy inhibiting the deposit of oxides on the rolls by the strip, and controlling the amount of reducing gas supplied so as to leave the atmosphere of said zone generally oxidizing in charact'er.

HARRY F. sHAfNN-N:

assiettes cited the fue ai this patent UNITED STATES PA'I'ENTS 

